Question

你好我有问题请看我的代码：

  public void showfal() {

    Cursor cu = database.rawQuery("SELECT * FROM fal WHERE startdate = 'G.todaydate'", null);

    while (cu.moveToNext()) {

        farvardin.add(cu.getString(cu.getColumnIndex("farvardin")) + "");
        ordibehesht.add(cu.getString(cu.getColumnIndex("ordibehesht")) + "");

        khordad.add(cu.getString(cu.getColumnIndex("khordad")) + "");
        tir.add(cu.getString(cu.getColumnIndex("tir")) + "");
        mordad.add(cu.getString(cu.getColumnIndex("mordad")) + "");
        shahrivar.add(cu.getString(cu.getColumnIndex("shahrivar")) + "");
        mehr.add(cu.getString(cu.getColumnIndex("mehr")) + "");
        aban.add(cu.getString(cu.getColumnIndex("aban")) + "");
        azar.add(cu.getString(cu.getColumnIndex("azar")) + "");
        dey.add(cu.getString(cu.getColumnIndex("dey")) + "");
        bahman.add(cu.getString(cu.getColumnIndex("bahman")) + "");
        esfand.add(cu.getString(cu.getColumnIndex("esfand")) + "");

    }

    cu.close();
}

当我调用showfal（）时，我收到::

    08-07 11:52:00.545: E/AndroidRuntime(6362): FATAL EXCEPTION: main
08-07 11:52:00.545: E/AndroidRuntime(6362): java.lang.RuntimeException: Unable to start activity ComponentInfo{ir.aradmobaile.mhd.fal/ir.aradmobaile.mhd.fal.Activity_dailyfal}: java.lang.NullPointerException
08-07 11:52:00.545: E/AndroidRuntime(6362):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at android.os.Looper.loop(Looper.java:137)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at android.app.ActivityThread.main(ActivityThread.java:5041)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at java.lang.reflect.Method.invokeNative(Native Method)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at java.lang.reflect.Method.invoke(Method.java:511)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at dalvik.system.NativeStart.main(Native Method)
08-07 11:52:00.545: E/AndroidRuntime(6362): Caused by: java.lang.NullPointerException
08-07 11:52:00.545: E/AndroidRuntime(6362):     at ir.aradmobaile.mhd.fal.Activity_dailyfal.showfal(Activity_dailyfal.java:167)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at ir.aradmobaile.mhd.fal.Activity_dailyfal.onCreate(Activity_dailyfal.java:39)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at android.app.Activity.performCreate(Activity.java:5104)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
08-07 11:52:00.545: E/AndroidRuntime(6362):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
08-07 11:52:00.545: E/AndroidRuntime(6362):     ... 11 more
08-07 11:57:00.549: E/InputDispatcher(368): channel '534453b4 ir.aradmobaile.mhd.fal/ir.aradmobaile.mhd.fal.MainActivity (server)' ~ Channel is unrecoverably broken and will be disposed!
08-07 11:57:00.549: E/InputDispatcher(368): channel '5355de34 Toast (server)' ~ Channel is unrecoverably broken and will be disposed!


public class Activity_dailyfal extends MainActivity {

public static Database          db;
public SQLiteDatabase database;


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.layout_fourth);
    db = new Database(this);
    db.database();
    db.open();
    showfal();

}

这是我的数据库活动：

    package ir.aradmobaile.mhd.fal;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class Database扩展了SQLiteOpenHelper {

//    public final String   path = "data/data/ir.aradmobaile.dabiri.fal/databases/"; // adresi ke data barname mire dakhelesh
public final String   Name = "arad_db"; // name of database
public SQLiteDatabase mydb;

private final Context mycontext;

公共数据库（上下文上下文）{

    super(context, "arad_db", null, 1);//set name of data base
    mycontext = context;

}


@Override
public void onCreate(SQLiteDatabase arg0) {

}


@Override
public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
    // TODO Auto-generated method stub

}


public void database() {

    boolean checkdb = checkdb();

    if (checkdb) {
        // means database exist

    } else {
        // means database not exist
        this.getReadableDatabase();

        try {
            copydatabase();
        }
        catch (IOException e) {

        }

    }

}


public void open() {

    mydb = SQLiteDatabase.openDatabase(G.DIR_DATABASE + Name, null, SQLiteDatabase.OPEN_READWRITE);

}


@Override
public void close() {
    mydb.close();
}


public boolean checkdb() {

    SQLiteDatabase db = null;
    try {
        db = SQLiteDatabase.openDatabase(G.DIR_DATABASE + Name, null, SQLiteDatabase.OPEN_READONLY);
    }
    catch (SQLException e)
    {

    }
    return db != null ? true : false;

}


// baraye copy kardan az dakhel barname(assets) be  database
public void copydatabase() throws IOException {
    OutputStream myOutput = new FileOutputStream(G.DIR_DATABASE + Name);
    byte[] buffer = new byte[1024];
    int length;

    InputStream myInput = mycontext.getAssets().open("arad_db");
    while ((length = myInput.read(buffer)) > 0) {
        myOutput.write(buffer, 0, length);
    }
    myInput.close();
    myOutput.flush();
    myOutput.close();
}


public String Display(int row, int fild) {
    Cursor cu = mydb.query("push", null, null, null, null, null, null);
    cu.moveToPosition(row);
    String name = cu.getString(fild);
    return name;
}


public String Display2(int row, int fild) {
    Cursor cu = mydb.query("json_length", null, null, null, null, null, null);
    cu.moveToPosition(row);
    String name = cu.getString(fild);
    cu.close();
    return name;
}


public String Display3(int row, int fild) {
    Cursor cu = mydb.query("fal", null, null, null, null, null, null);
    cu.moveToPosition(row);
    String name = cu.getString(fild);
    cu.close();
    return name;
}


public String Display4(int row, int fild) {
    Cursor cu = mydb.query("json_length2", null, null, null, null, null, null);
    cu.moveToPosition(row);
    String name = cu.getString(fild);
    cu.close();
    return name;
}


public void inser(int id, String name, String user, String pass, String jj) {

    ContentValues cv = new ContentValues();
    cv.put("push_id", id);
    cv.put("push_title", name);
    cv.put("push_subject", user);
    cv.put("push_body", pass);
    cv.put("push_url", jj);
    mydb.insert("push", "push_id", cv);

}


public void inser2(int id, int id2) {

    ContentValues cv = new ContentValues();
    cv.put("id_num", id);
    cv.put("json_length", id2);
    mydb.insert("json_length", "id_num", cv);

}


public void inser3(int id, String far, String ord, String kho, String tir, String mor, String sha, String meh, String aba, String aza, String dey, String bah, String esf, String date) {

    ContentValues cv = new ContentValues();
    cv.put("id", id);
    cv.put("farvardin", far);
    cv.put("ordibehesht", ord);
    cv.put("khordad", kho);
    cv.put("tir", tir);
    cv.put("mordad", mor);
    cv.put("shahrivar", sha);
    cv.put("mehr", meh);
    cv.put("aban", aba);
    cv.put("azar", aza);
    cv.put("dey", dey);
    cv.put("bahman", bah);
    cv.put("esfand", esf);
    cv.put("startdate", date);
    mydb.insert("fal", "id", cv);

}

我检查了我的桌子，这里有2条记录。我困惑哪里是我的错？

Answer 1

我认为你的查询不对。

在访问之前检查游标是否为null。

喜欢：while (cu != null && cu.moveToNext()) {

Answer 2

而是使用cloumn的名称是否正确。

Cursor cu = database.rawQuery("SELECT * FROM fal WHERE startdate='"+ G.todaydate+"';", null);

是的，在访问之前检查是否（cursor！= null）。

调用Cursor时，Android sqlite数据库空指针异常

2 个答案: